1. Field of the Invention
The present invention relates to a method and an apparatus for producing binary image data of a halftone dot image from multi-digital image data of a contone image (or a continuous tone image).
2. Description of the Prior Art
In color printing process, direct scanners having a dot generator are widely used for electronically performing dot generation operation, by which contone image are converted into halftone dot images. Dot generator includes a hardware type and a software type.
A hardware dot generator includes a specific electronic circuit with a comparator and a screen pattern memory. The screen pattern memory stores a basic pattern or patterns having threshold level data. The hardware dot generator compares a multi-digital image signal with the basic pattern or patterns with the comparator thereof and forms halftone dots corresponding to the level of the image signal.
Although the hardware dot generator has an advantage of high speed processing, it lacks versatility to form halftone dots for special conditions other than standard halftone dots. For example, the hardware dot generator cannot form halftone dots having rather complicated shapes.